Modern engine electronics systems and associated control methods enable ever greater optimization of the efficiency of an internal combustion engine. In the case of Otto engines the timing position of the ignition point plays an essential role therein. The efficiency or torque produced by an Otto engine has a maximum which is dependent on the ignition advance angle. For the sake of protecting components, however, this optimum ignition advance angle can only be set to a few operating points. In large parts of the operating range of the internal combustion engine, operation of the internal combustion engine at this optimum ignition advance angle would lead to engine knocking and thus eventually to damage to the internal combustion engine. For this reason, in these operating ranges, the internal combustion engine must be operated with an ignition advance angle at which the efficiency is reduced. In the attempt to reach the highest efficiency level possible for each operating point, whilst simultaneously avoiding damage, modern engine control concepts include ‘knocking control systems’ which detect engine knocking and adjust the set ignition advance angle accordingly. By this means, the set ignition advance angle can be made to lie very close to the knocking limit of the engine.
In order to detect engine knocking, a knocking sensor can be integrated on or in the engine. The knocking events typically take place within a limited crankshaft angular interval about the top dead centre point of the piston. In order to ensure reliable detection of a knocking event by means of the sensor, it is necessary to restrict evaluation of the sensor signal to the narrowest possible crankshaft angular interval within which knocking could possibly occur. The narrower the crankshaft angular interval for evaluating the sensor signal, the more reliably knocking can be detected and separated from normal combustion. However, the knocking tendency of an internal combustion engine is influenced by a large number of factors, such as the ambient air temperature, the engine temperature, the exhaust gas recirculation rate and the fuel quality.
In a known method, these factors are permanently kept available for defining the evaluating interval of the knocking sensor signal, so that it is always substantially longer than the actual knocking event. Apart from the actual knocking events, the signal from the knocking sensor which is to be evaluated therefore also has the basic engine noise that remains even despite filtration, together with other interfering signals, which negatively influence the accuracy of knocking detection. The interfering signals include, for example, sounds from the opening and closing of the inlet and outlet valves.